Prior to the use of springs, seat cushions were simply stuffed with matting, fill or other soft fibers. After a period of use, the cushion stuffing would settle, often resulting in a hard, lumpy, uncomfortable cushion.
The advent of the coil spring solved many of the prior problems. The early coil springs were placed in a frame under the seat cushion padding in a sufficient number of rows to provide proper seating support. The coil springs advantageously provided a consistent spring resilience throughout the seating area. However, this manner of providing cushion seating was expensive due to the large number of coil springs needed to support a cushion in a consistent manner.
The development of the sinuous spring caused many manufacturers to adopt this spring as an economical substitute for the prohibitively priced coil spring structure. The sinuous springs have a zig-zag pattern and are generally disposed in an upwardly bending arc between two parallel sides of a frame. Rows of sinuous wire springs are generally attached in a parallel alignment between the front and rear walls of cushion seating frames, offering both comfort and resilience. While the substitution of sinuous springs for coil springs reduced the amount of wire and the cost of the springs by between 60 and 80%, the firmness and comfort offered by only the rows of sinuous wires did not meet the needs of all. Heavier people found that the sinuous wire springs designed for people of average weight do not provide the desired resilience and have a tendency to bottom out. "Bottoming out" as used in this application, is a term of art generally referring to that condition in which the force which has been applied to the springs in a cushion exceeds the ability of the springs to resiliently resist the applied force, thus causing the springs to sag to a position in which further travel of the springs is restrained by supporting structure or by the fully extended springs. The use of stronger, stiffer springs, while providing more comfort to heavier persons, proved to be too hard and uncomfortable for lighter persons. The problem of providing proper support and resilience in cushion seating for heavier persons has also been compounded by the fact that the average person of today is bigger and heavier than the average person of 40 years ago. In addition, today's consumer is more sophisticated and demanding than in the past. Thus, the requirements for seat cushion constructions which can provide acceptable levels of support and comfort to a broader spectrum of people are more demanding today than in the past.
Attempts to overcome the aforementioned problems and to provide cushion seating with comfort and resilience have included the combination of sinuous springs and coil springs. The coil springs were often placed between a flexible base support and the sinuous springs to provide more resilience to the sinuous spring. For example, U.S. Pat. No. 2,234,253 discloses a spring cushion construction which includes a plurality of parallel-disposed sinuous springs with coil springs disposed beneath them. The lower ends of the coil springs are supported by another row of sinuous springs extending transversely to the top row. U.S. Pat. No. 2,280,912 discloses a spring arrangement for bedsprings, boxsprings, etc., having a plurality of parallel sinuous springs form the top surface of the cushion spring assembly. The sinuous springs are secured to tapered coil springs which are in turn secured to a lower level of sinuous springs transversely positioned with respect to the top sinuous springs. U.S. Pat. No. 4,597,566 discloses another form of spring cushion seating in which coil springs are placed between a plane of nonresilient wires, supported on the frame by helical edge springs, and a base bar. However, this patent does not provide the feel traditionally associated with the use of sinuous springs.
Furthermore, traditional spring cushion seating is generally heavy due to the amount and composition of the structure used to provide support to the sinuous and coil springs. While the cushion spring structures of the prior art solved some of the problems inherent with sinuous wire-only spring structures by reducing the tendency to bottom out, the prior art structure still lacks the requisite combination of firmness and deep resilience which is desirable in cushion seating today and that, in manufacture, results in a relatively lightweight finished product.